Decision to Leave

Detective Hae-Jun is stationed in the bustling city of Busan, where his demanding job keeps him away from his wife, Jung-An, who he sees only once a week. This isolation and exhaustion fuel his insomnia, leading him to pursue his work with an intensified fervor.

Hae-Jun, alongside his partner Soo-Wan, investigates the mysterious death of Ki Do Soo, a retired immigration officer. Ki's body is found at the base of a mountain he often climbed, prompting the detectives to dive deeper into the circumstances surrounding his demise.

The investigation leads Hae-Jun and Soo-Wan to interview Ki's young wife, Seo-Rae, a Chinese immigrant and caregiver. Her subdued reaction to her husband's death, coupled with her physical injuries and a tattoo of his initials, raise suspicions about her potential involvement in the tragedy.

Intrigued and unsettled by Seo-Rae, Hae-Jun begins to conduct nighttime surveillance outside her home. His fixation grows as he imagines the life unfolding inside her apartment, becoming more entwined in her complex world.

During their investigation, Seo-Rae reveals a dark part of her past: she admitted to hastening her mother's death with fentanyl to fulfill her mother’s final wishes. This revelation highlights the emotional turmoil she has experienced, adding layers to her character and her motivations.

Hae-Jun and Soo-Wan find incriminating letters written by Ki that expose his corruption as an immigration officer. These letters suggest that he was deeply troubled and considering suicide, which sheds new light on the case and alleviates Seo-Rae’s initial suspicion.

As Hae-Jun tells Seo-Rae she is no longer a suspect, they begin to form a bond that transcends the investigation. Their relationship deepens through shared moments, including visits to a Buddhist temple, and they start to confide in each other.

While substituting for one of Seo-Rae's clients, Hae-Jun discovers that both Seo-Rae and the client have identical smartphones. This unsettling revelation prompts him to piece together the timeline of Ki's death, leading him to suspect foul play.

Hae-Jun arrives at a painful realization: Seo-Rae had orchestrated Ki's murder and faked a suicide note. Confronted with this betrayal, Hae-Jun feels his professional integrity is irreparably damaged, creating a rift between him and Seo-Rae.

Thirteen months later, Hae-Jun relocates to Ipo to start anew with his wife, Jung-An. However, he grapples with depression and insomnia, still haunted by his past with Seo-Rae and the unsolved mysteries surrounding her.

While visiting a fish market in Ipo, Hae-Jun unexpectedly comes face-to-face with Seo-Rae, who is now married to business tycoon Im Ho-Shin. Their meeting rekindles their complicated past, and soon after, Ho-Shin's body is discovered.

After Ho-Shin's mysterious death in the family swimming pool, Seo-Rae offers a nonchalant explanation that raises Hae-Jun's distrust. A confession from a Chinese immigrant claims to have killed Ho-Shin, but Hae-Jun's doubts linger regarding Seo-Rae's involvement.

The strain of ongoing suspicions puts a severe strain on Hae-Jun's marriage, leading Jung-An to confront him about his apparent connection to Seo-Rae. Hae-Jun learns that Ho-Shin had threatened Seo-Rae with exposure, unveiling hidden layers of their relationship.

At the mountain, Hae-Jun and Seo-Rae confront their feelings as emotions run high, resulting in an unexpected kiss. Despite their tumultuous history, this moment underscores the complexity of their bond intertwined with grief and longing.

As Seo-Rae decides to immerse herself in the ocean, Hae-Jun discovers a phone that reveals incriminating evidence. He reaches the beach, but when he calls for her, he tragically realizes the depths of her sacrifice, standing unknowingly on her unmarked grave.